Web transport apparatus and solution casting process

ABSTRACT

A pin tentering apparatus as web transport apparatus includes a tentering mechanism for transporting self-supporting cast film by retaining web edge portions of the cast film. A gas flow device blows evaporative gas to the cast film being transported, to float the cast film. A static pressure adjuster lowers static pressure of the evaporative gas to a web middle portion with respect to a web width direction of the cast film, to regularize distribution of the static pressure in the web width direction. In the gas flow device, a blower duct introduces the evaporative gas. A nozzle plate is positioned at a front end of the duct, and has nozzles which blow the evaporative gas. Preferably, the static pressure adjuster includes an exhaust device, disposed to face the web middle portion between the plural nozzles, for exhausting the evaporative gas.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a web transport apparatus and solution casting system. More particularly, the present invention relates to a web transport apparatus and solution casting system in which web or cast film produced continuously can be prevented from protrusion with a curve even in application of gaseous medium to the web.

2. Description Related to the Prior Art

Polymer film is widely used as optical functional film because of high transparency, flexibility and possibility for lightweight feature and reduction of the thickness. Among various examples of polymer films, cellulose ester film produced from cellulose acylate or other cellulose esters is characterized in high performance with rigidity and low birefringence. The cellulose ester film is used as photosensitive material for photography, and also as protective film, optical compensation film and the like for a panel shaped polarizer element as a constituent of a liquid crystal display device (LCD).

Solution casting is a typically used method of producing the cellulose ester film. At first, viscous solution or dope containing cellulose ester and solvent is prepared, and cast from a casting die on to a casting support. Cast film is formed. When the cast film comes to have a self-supporting property, a self-supporting cast film is stripped from the casting support. A tentering machine is supplied with the self-supporting cast film, clamps web edges of the self-supporting cast film to transport the same, which is dried and becomes the cellulose ester film. A web edge slitter slits web edges portions of the cellulose ester film, which is dried finally by a dryer and wound by a winder.

JP-A 2003-260741 discloses a tentering machine, specifically a pin tentering machine for use with the self-supporting cast film having a high solvent amount. A duct is disposed lower or higher than the cellulose ester film and blows evaporative gas to the self-supporting cast film. The self-supporting cast film is transported and dried at the same time.

If the self-supporting cast film is transported in flotation by the duct, force of gas to a web middle portion as viewed in a web width direction. The web middle portion is likely to protrude convexly while the self-supporting cast film is transported. Although there is a social requirement of a large area type of liquid crystal display panel, no known technique is effective in preventing incidental protrusion of the web middle portion of which a web width may be considerably great. Specifically, a solution casting system should be suitable for a great width structure. Distribution of the static pressure of the atmosphere under the self-supporting cast film is still wider than that according to the widely used tentering machine, the distribution corresponding to that of the force of floating of the self-supporting cast film in the tension drying. However, it is impossible in known techniques to solve problems of instability of transport of the self-supporting cast film and degradation of the self-supporting cast film as product.

SUMMARY OF THE INVENTION

In view of the foregoing problems, an object of the present invention is to provide a web transport apparatus and solution casting system in which web or cast film produced continuously can be prevented from protrusion with a curve even in application of gaseous medium to the web.

In order to achieve the above and other objects and advantages of this invention, a web transport apparatus includes a transport mechanism for transporting web by retaining web edge portions of the web. A gas flow device blows gaseous medium to the web being transported, to float the web. A static pressure adjuster lowers static pressure of the gaseous medium to a web middle portion of the web with respect to a web width direction thereof, to regularize distribution of the static pressure in the web width direction.

The gas flow device includes a duct for introducing the gaseous medium. A nozzle plate is positioned at a front end of the duct, has a nozzle, for blowing the gaseous medium through the nozzle.

The static pressure adjuster limits the distribution of the static pressure to a value equal to or more than −200% and equal to or less than +200% per unit area of said web.

The gaseous medium is evaporative gas, and the transport mechanism is constituted by a tentering mechanism.

The static pressure adjuster controls a flow rate of the gaseous medium in the gas flow device with respect to the web width direction.

The nozzle is constituted by plural nozzles. The static pressure adjuster includes an exhaust device, disposed to face the web middle portion between the plural nozzles, for exhausting the gaseous medium.

The exhaust device is so constructed that a flow rate of exhausting the gaseous medium is variable.

The plural nozzles include a first nozzle group of nozzles opposed to the web edge portions. A second nozzle group of nozzles is opposed to the web middle portion, and offset from the exhaust device.

The static pressure adjuster includes a recess, formed in the nozzle plate, and opposed to the web middle portion.

The nozzle is constituted by plural nozzles including a first nozzle group of nozzles opposed to the web edge portions. A second nozzle group of nozzles is opposed to the web middle portion, for operating at a smaller flow rate of the gaseous medium than a flow rate of the gaseous medium of the first nozzle group, to constitute the static pressure adjuster.

The duct includes a first duct section for introducing the gaseous medium to the first nozzle group. A second duct section introduces the gaseous medium to the second nozzle group. The static pressure adjuster controls the duct by setting the flow rate smaller for the second duct section than for the first duct section.

In a preferred embodiment, a total aperture area of the second nozzle group is smaller than a total aperture area of the first nozzle group.

In another preferred embodiment, a number of the nozzles in the second nozzle group is smaller than a number of the nozzles in the first nozzle group.

The nozzle plate is constituted by plural nozzle plates, arranged in a transport direction of the web at a regular interval, disposed respectively to extend in the web width direction, for blowing the gaseous medium. The static pressure adjuster includes a movable plate portion disposed between the nozzle plates, a distance of the movable plate portion from the web being variable.

The movable plate portion is set farther from the web than the nozzle plates.

Furthermore, an exhaust device is disposed through the movable plate portion, for exhausting the gaseous medium.

The transport mechanism includes first and second tenter pin groups, disposed to face respectively the web edge portions, respectively including plural tenter pins for piecing the web edge portions. A moving device endlessly moves the first and second tenter pin groups along the web edge portions, to transport the web.

The web is cast film, formed by casting cellulose ester solution containing cellulose ester and solvent, and having a self-supporting property.

A content of the solvent contained in the cast film is equal to or more than 130 wt. %.

According to another aspect of the invention, a solution casting process includes a step of casting cellulose ester solution on to an endlessly traveling support, to form cast film. The cast film is stripped from the support. The cast film is transported by retaining web edge portions of the cast film. Gaseous medium is blown to the cast film being transport for flotation. Static pressure of the gaseous medium to a web middle portion of the cast film is lowered with respect to a web width direction thereof, to regularize distribution of the static pressure in the web width direction.

Accordingly, web or cast film produced continuously can be prevented from protrusion with a curve even in application of gaseous medium to the web, because the static pressure of gaseous medium at the web middle portion is lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will become more apparent from the following detailed description when read in connection with the accompanying drawings, in which:

FIG. 1 is an explanatory view in side elevation illustrating a solution casting system;

FIG. 2 is a cross section illustrating one preferred gas flow device having an exhaust conduit;

FIG. 3 is a perspective view illustrating the gas flow device of FIG. 2;

FIG. 4 is a cross section illustrating one preferred gas flow device having a static pressure adjusting recess;

FIG. 5 is a perspective view illustrating the gas flow device of FIG. 4;

FIG. 6 is a cross section illustrating one preferred gas flow device having plural controllable duct sections;

FIG. 7 is a perspective view illustrating the gas flow device of FIG. 6;

FIG. 8 is a perspective view illustrating one preferred gas flow device having movable plate portions;

FIG. 9 is a cross section illustrating the gas flow device of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE PRESENT INVENTION

In FIG. 1, a solution casting system 10 of the invention is illustrated. The solution casting system 10 includes a casting chamber 11, a transition region 12, a pin tentering machine 13, a clip tentering machine 14, web edge slitters 15 a and 15 b, a dryer 16, a cooler 17 and a winder 18.

The casting chamber 11 includes a feed block 22, a casting support drum 23, a casting die 24, a stripping roller 26, a solvent condenser 27 and a solvent recovery device 28. The feed block 22 is supplied by a dope producing apparatus 20 with dope or viscous solution. The casting die 24 is adapted to casting the dope on to the casting support drum 23. The stripping roller 26 strips cast film 25 of cellulose ester from the casting support drum 23 to deliver self-supporting cast film 25 a as web. The solvent condenser 27 condenses and liquefies solvent gas evaporated from the cast film 25. The solvent recovery device 28 recovers the liquefied solvent. A heat exchange medium circulator (not shown) is connected with the casting support drum 23, and conditions the surface temperature of the casting support drum 23 at a predetermined level by flow of heat exchange medium through its conduit. A temperature adjuster 30 is associated with the casting chamber 11 for conditioning its inner temperature.

A flow conduit is formed in the feed block 22 for dope. The form of the flow conduit can be modified to adjust the structure of the cast film 25. A decompressor 32 with a decompression chamber is associated with the casting die 24. A rear side or upstream side of the bead of the dope is decompressed by the decompressor 32, the bead flowing from the ejection slot down to the casting support drum 23. This is for stabilizing the contact of the bead with the casting support drum 23. A jacket (not shown) is associated with the decompressor 32 for adjusting the inner temperature with heat exchange medium.

The casting support drum 23 is a continuously rotatable drum of a stainless steel. A surface of the casting support drum 23 is finished by polishing. This is effective in forming the cast film 25 with high flatness on the casting support drum 23. Note that a casting support element may be a different form other than the casting support drum 23. For example, a casting support may be an endless belt, which can be turned about by two driving rollers. A preferable width of the casting support drum 23 can be 1.1-2.0 times as much as a casting width of the dope. The material of the casting support drum 23 is preferably has sufficient strength and resistance to corrosion, for example, stainless steel or other materials.

The shape, material, size and the like of the casting die 24 are not limited. A coat hanger type of die is preferable for the casting die 24 so a casting width of the dope can be kept at a predetermined size. A preferable size of the slot in the casting width direction is 1.1-2.0 times as long as the casting width of the dope. A preferable material of the casting die 24 can be stainless steel of a type of precipitation hardening owing to the durability, heat resistance and the like. Also, the material of the casting die 24 has the corrosion resistance sufficient for prevention of pitting on the gas-liquid interface even after dipping in a liquid mixture of dichloromethane, methanol and water for three (3) months. Desirably, a corrosion resistance of the material should be equal to that of SUS 316 steel according to forced corrosion test in electrolytic aqueous solution. In view of heat resistance, the material can have a coefficient of thermal expansion of 2×10⁻⁵ (/deg. C.) or less.

A hardened layer or case can be preferably formed on the end of the slot lip of the casting die 24. Various methods for forming the hardened layer or case can be used, including application of a ceramic coating, a hard chromium plating, and processing of nitriding. In case of using the ceramic coating, the material of the ceramic coating should have suitability for grinding, low porosity, low fragility, high resistance to corrosion, suitability for adhesion to the casting die 24, and property of small adhesion to the dope. Specifically, WC (tungsten carbide), Al₂O₃, TiN, Cr₂O₃ and the like can be used, among which WC is particularly preferable. A thermal spray process can be used for applying a WC coating.

A contact surface of the casting die 24 for the dope is preferably a polished or abraded surface for high smoothness to form the cast film 25 with high flatness. An absorption device (not shown) is preferably connected to a slot edge portion of the casting die 24, and absorbs air at an edge flow rate of 1-100 liters per minute. Thus, it is possible to reduce an air flow which might cause unevenness on surfaces of the bead.

A great number of transport rollers 35 are arranged in the transition region 12 and transport the self-supporting cast film 25 a to the pin tentering machine 13 after stripping from the casting support drum 23. A fan or blower 36 is disposed higher than a path of the self-supporting cast film 25 a, and blows evaporative gas to reduce the contained solvent from the self-supporting cast film 25 a by drying.

In FIG. 2, the pin tentering machine 13 includes an endless chain 40, a tenter pin plate 42, and tenter pins 43 in two tenter pin groups, those being included in a transport mechanism. Each one of rails 39 support the endless chain 40 for endless traveling in a circulating manner. The tenter pin plate 42 is fastened on the endless chain 40. The tenter pins 43 are disposed to project from the tenter pin plate 42. When the self-supporting cast film 25 a from the transition region 12 enters the pin tentering machine 13, the tenter pins 43 are pierced in web edge portions 45 of the self-supporting cast film 25 a, which is transported in a transport direction X according to the endless chain 40 and the tenter pin plate 42. A shifting mechanism 44 operates to shift the rails 39 in a web width direction Y of the self-supporting cast film 25 a. Thus, the width of the self-supporting cast film 25 a is adjustable according to drying.

In FIGS. 2 and 3, a gas flow device 48 for drying is included in the pin tentering machine 13 and disposed under a path for the self-supporting cast film 25 a. The gas flow device 48 includes a blower duct 50, a gas source 52, apertures of an exhaust device 53 as static pressure adjuster, and an exhaust flow rate control unit 54. In a lower surface 55 of the duct 50, an inlet opening 55 a for inlet fitting is formed. Gaseous medium 56 or evaporative gas is supplied by the gas source 52, and enters the duct 50 through the inlet opening 55 a. A nozzle plate 57 is positioned on a top of the duct 50 in the gas flow device 48. Plural nozzles 57 a are formed in the nozzle plate 57, are disposed at a regular interval, and blow out the gaseous medium 56. Note that the self-supporting cast film 25 a in the pin tentering machine 13 has a volatile content or residual solvent content which is, for example, equal to or more than 130 wt. %.

The exhaust device 53 is positioned at the center of the duct 50 relative to the width direction, and extends from the nozzle plate 57 to the lower surface 55. Plural exhaust conduits 53 a in the exhaust device 53 are arranged in the direction X at a regular interval. The exhaust conduits 53 a are disposed in the nozzle plate 57 of the duct 50 and opposed to the web middle portion of the self-supporting cast film 25 a as viewed in the width direction. Gaseous medium 56 a or evaporative gas, included in the gaseous medium 56 under the self-supporting cast film 25 a, is exhausted by the exhaust conduits 53 a in the exhaust device 53. Also, the exhaust device 53 includes an exhaust opening 53 b. The exhaust opening 53 b is formed in the lower surface 55 of the duct 50, and passes the gaseous medium 56 a toward the outside. The exhaust flow rate control unit 54 controls an exhaust flow rate of the gaseous medium 56 a from the exhaust opening 53 b. Note that indication of reference numerals in FIG. 3 is simplified for convenience, for example, the exhaust device 53, the exhaust conduits 53 a, the gaseous medium 56 and 56 a and the nozzles 57 a.

Thus, the static pressure of the portion opposed to the web middle portion of the self-supporting cast film 25 a in the lower space can be lowered by exhausting the gaseous medium 56 a through the exhaust conduits 53 a which are positioned to face the web middle portion. The distribution of the static pressure under the self-supporting cast film 25 a can be limited to a range from −200% to +200% of the weight per area of the self-supporting cast film 25 a, because the static pressure of the web middle portion is set equal to the static pressure of other portions. Note that the use of the unit of the weight per area of the self-supporting cast film 25 a for the distribution of the static pressure is because of the finding in that the static pressure of flotation required for transport with floating should be the weight of the self-supporting cast film 25 a.

The distribution of the static pressure can be regularized under the self-supporting cast film 25 a. It is possible to prevent the self-supporting cast film 25 a from protruding convexly upwards in the pin tentering machine 13. Quality of the cellulose ester film will be kept high.

An aperture of the exhaust conduits 53 a may not be quadrilateral. For example, the aperture of the exhaust conduits 53 a may be elliptical. Also, an exhaust conduit can be formed with a nozzle-shaped circular aperture, and can be disposed regularly and opposed to the web middle portion of the self-supporting cast film 25 a. In the embodiment, the lower surface 55 of the duct 50 is formed similarly to the nozzle plate 57. However, the nozzle plate 57 may be formed with an area larger than an area of the lower surface 55. For this structure, the exhaust device 53 is shaped with a larger area of the exhaust conduits 53 a than an area of the exhaust opening 53 b. Furthermore, an area adjusting mechanism can be added for adjusting an aperture area of the exhaust conduits 53 a. The static pressure distribution under the self-supporting cast film 25 a may be regularized by lowering the static pressure under the web middle portion.

In the embodiment, the gas flow device 48 is disposed under the path of the self-supporting cast film 25 a. However, an upper gas flow device for drying with a blower duct can be disposed higher than the path of the self-supporting cast film 25 a, and blow evaporative gas down to the same.

In FIG. 1, the clip tentering machine 14 is positioned downstream from the pin tentering machine 13, clamps and transports the web edge portions 45 of the self-supporting cast film 25 a, and also dries the same. Thus, cellulose ester film 37 is obtained. The web edge slitter 15 a is disposed between the pin tentering machine 13 and the clip tentering machine 14, and slits the web edge portions 45 of the cellulose ester film 37 exited from the pin tentering machine 13. The web edge slitter 15 b is disposed between the clip tentering machine 14 and the dryer 16, and slits the web edge portions 45 from the cellulose ester film 37 exited from the clip tentering machine 14. A film crusher 65 is connected with the web edge slitters 15 a and 15 b, and grinds the web edge portions 45 into chips. The cellulose ester film 37 being slitted is moved to the dryer 16. A great number of rollers 67 are contained in the dryer 16, and transport the cellulose ester film 37 which is dried at the same time. The cellulose ester film 37 from the dryer 16 is transported to the cooler 17, and cooled down to approximately the room temperature.

An adsorption solvent recovery device 69 is connected with various elements which are the transition region 12, the pin tentering machine 13, the clip tentering machine 14 and the dryer 16. The adsorption solvent recovery device 69 recovers gaseous solvent from those elements by adsorption. The recovered solvent is reused as raw material for the dope.

A winding roller 70 is included in the winder 18, and winds the cellulose ester film 37 from the cooler 17 in a form of a roll. Also, a press roller 71 in the winder 18 controls tension exerted in the cellulose ester film 37 during the winding on to the winding roller 70.

Finally, the cellulose ester film 37 with high flatness is obtained stably and rapidly. A web width of the cellulose ester film 37 is preferably equal to or more than 1,400 mm and equal to or less than 2,500 mm. The feature of the invention is effective also if the width is over 2,500 mm. A thickness of the cellulose ester film 37 as product is equal to or more than 20 microns and equal to or less than 100 microns, and preferably equal to or more than 20 microns and equal to or less than 80 microns, and desirably equal to or more than 30 microns and equal to or less than 80 microns.

Another preferred embodiment is hereinafter described. Elements similar to those of the above embodiment are designated with identical reference numerals. In FIGS. 4 and 5, a gas flow device 75 for drying is disposed under a path for the self-supporting cast film 25 a in the pin tentering machine 13. The gas flow device 75 includes a blower duct 76 and a gas source 78 in the gas flow device, which supplies gaseous medium 77 or evaporative gas to the duct 76. A nozzle plate 80 is an element positioned at the top of the duct 76. A static pressure adjusting recess 82 is formed in the nozzle plate 80, opposed to the web middle portion of the self-supporting cast film 25 a, and extends in the transport direction X. Nozzles 82 a are formed in the static pressure adjusting recess 82, and blow the gaseous medium 77. Nozzles 80 a are formed in portions of the nozzle plate 80 except for the static pressure adjusting recess 82 in the duct 76, are positioned regularly, and blow the gaseous medium 77. There is a lower surface 83 of the duct 76. An inlet opening 83 a for inlet fitting is formed in the lower surface 83 for supply of the gaseous medium 77 from the gas source 78.

The static pressure adjusting recess 82 is formed in the nozzle plate 80 and extends in the X direction of the duct 76. The nozzles 82 a are formed in the portion of the static pressure adjusting recess 82. Thus, a distance from the nozzles 82 a to the self-supporting cast film 25 a is longer than that from the nozzles 80 a to the same. A space on the nozzle plate 80 opposed to the web middle portion of the self-supporting cast film 25 a is defined larger, so that a static pressure at the web middle portion of the self-supporting cast film 25 a can be lower. Thus, the static pressure of the web middle portion becomes approximately equal to the static pressure of the web edge portions. The static pressure distribution of the atmosphere under the self-supporting cast film 25 a is regulated in a range from −200% to +200% of the weight per area of the self-supporting cast film 25 a. Therefore, the web middle portion of the self-supporting cast film 25 a in the pin tentering machine 13 is reliably prevented from protruding convexly upwards in the transport. Note that indication of reference numerals in FIG. 5 is simplified for convenience, for example, the gaseous medium 77 and the nozzles 80 a and 82 a.

The static pressure adjusting recess 82, as viewed in the section, is formed in the V shape in FIGS. 4 and 5, but may be formed in another suitable shape, such as a semi-circular shape, a quadrilateral shape and the like. Also, it is possible instead of the static pressure adjusting recess 82 to use modified forms of nozzles opposed to the web middle portion for the purpose of lowering the static pressure in the middle. To modify the nozzles, their arrangement, shapes, and the like may be suitably changed. Specifically, the number of the nozzles in the portion opposed to the web middle portion can be set smaller than the number of the nozzles in portions opposed to the web edge portions. Also, a total area of openness of the nozzles in the portion opposed to the web middle portion can be set smaller than a total area of openness of the nozzles in portions opposed to the web edge portions. Furthermore, a depth adjusting mechanism may be added to adjust the depth of the static pressure adjusting recess 82, so as to change the volume of the space under the web middle portion of the self-supporting cast film 25 a. This is effective in regularizing the distribution of the static pressure.

Also, one or more projections may be formed on a nozzle plate of an upper gas flow device directed downwards, in place of the static pressure adjusting recess 82 in the nozzle plate 80 of the duct 76.

A still another preferred gas flow device 90 for drying is described. Elements similar to those of the above embodiments are designated with identical reference numerals. In FIGS. 6 and 7, the gas flow device 90 is disposed under a path of the self-supporting cast film 25 a in the pin tentering machine 13. The gas flow device 90 includes a blower duct 91, a first gas source 92 and a second gas source 93. The duct 91 is constituted by a first duct section 94 and a second duct section 95.

The first duct section 94 includes an inlet opening 97 for inlet fitting, and is provided with nozzles 98 in a nozzle plate. The inlet opening 97 is supplied with gaseous medium 96 or evaporative gas by the first gas source 92. The nozzles 98 blow the gaseous medium 96. The nozzles 98 are disposed regularly and opposed to the web middle portion of the self-supporting cast film 25 a. The second duct section 95 includes an inlet opening 101 for inlet fitting, and is provided with nozzles 102 in a nozzle plate. The inlet opening 101 is supplied with gaseous medium 100 or evaporative gas by the second gas source 93. The nozzles 102 blow the gaseous medium 100. The nozzles 102 are disposed regularly and opposed to portions of the self-supporting cast film 25 a except for its web middle portion. A flow rate control unit 92 a as static pressure adjuster is incorporated in the first gas source 92, and controls the flow in such a manner as to set a flow rate of the gaseous medium 96 smaller than that of the gaseous medium 100.

Note that a flow rate adjuster may be associated with the second gas source 93 for setting a flow rate of the gaseous medium 100 higher than that of the gaseous medium 96. Flow rate adjusters may be associated with respectively the first and second gas sources 92 and 93 for setting a flow rate of the gaseous medium 96 lower than that of the gaseous medium 100. Furthermore, a single gas source may be associated with both of the first and second gas sources 92 and 93. For this structure, a shape of the nozzles 102 can be determined differently from that of the nozzles 98.

A flow rate of the gaseous medium 96 toward the web middle portion of the self-supporting cast film 25 a is set smaller than that of the gaseous medium 100. In relation to the static pressure, static pressure on the underside of the web middle portion becomes lower locally. Thus, the static pressure of the web middle portion becomes approximately equal to the static pressure of the web edge portions. The static pressure distribution of the atmosphere under the self-supporting cast film 25 a is regulated in a range from −200% to +200% of the weight per area of the self-supporting cast film 25 a. Therefore, the web middle portion of the self-supporting cast film 25 a in the pin tentering machine 13 is reliably prevented from protruding convexly upwards in the transport. Note that indication of reference numerals in FIG. 7 is simplified for convenience, for example, the gaseous medium 96 and 100, and the nozzles 98 and 102.

In FIGS. 8 and 9, one preferred gas flow device 110 for drying is illustrated. Elements similar to those of the above embodiment are designated with identical reference numerals. The gas flow device 110 is disposed under the self-supporting cast film 25 a in the pin tentering machine 13. The gas flow device 110 includes a blower duct 111 and gaseous medium 112 or evaporative gas. A gas source 113 in the gas flow device supplies the duct 111 with the gaseous medium 112. Nozzle plates 115 are arranged in the direction X at a regular interval, and extend in the web width direction Y. Movable plate portions 116 as static pressure adjuster are disposed between the nozzle plates 115 alternatively and are arranged in the transport direction X regularly. A shifting mechanism 118 shifts the movable plate portions 116 in the vertical direction Z. Nozzles 115 a are formed in the nozzle plates 115, are arranged regularly, and blow the gaseous medium 112. Exhaust channels 116 a are formed in the movable plate portions 116 for exhausting the gaseous medium 112. Note that the exhaust channels 116 a may be omitted from the movable plate portions 116 according to a specific structure of the gas flow device 110.

The static pressure of flotation of the self-supporting cast film 25 a can be adjusted by suitably keeping the movable plate portions 116 shifted in the Z direction in combination with the nozzle plates 115 of a protruding form. Thus, the static pressure of the web middle portion becomes approximately equal to the static pressure of the web edge portions. The static pressure distribution of the atmosphere under the self-supporting cast film 25 a is regulated in a range from −200% to +200% of the weight per area of the self-supporting cast film 25 a. Therefore, the web middle portion of the self-supporting cast film 25 a of in the pin tentering machine 13 is reliably prevented from protruding convexly upwards in the transport. Note that indication of reference numerals in FIG. 8 is simplified for convenience, for example, the gaseous medium 112, the nozzle plates 115, the movable plate portions 116, the nozzles 115 a and the exhaust channels 116 a.

In the embodiments, the tentering machine for the transport is the pin tentering machine. However, a tentering machine in combination with the feature of the invention can be a clip tentering machine. Also, a web transport apparatus of the invention may be any suitable apparatus for transporting web of a continuous shape different from the self-supporting cast film 25 a.

In the above embodiments, nozzles are disposed in the matrix form in the nozzle plate. However, the gas flow device of the invention may be shaped in a bar form extending in the web width direction Y. The nozzles may be arranged in at least one nozzle array extending in the web width direction Y.

Further to the above embodiments, two or more gas flow devices having each nozzle plate can be used and arranged in the transport direction X. Each of the plural gas flow devices can include a number of plural gas flow units of a bar type.

In the above embodiments, a single dope is cast to form a polymer film of a single layer. In the solution casting of the invention, the dopes, namely two or more dopes, can be cast according to simultaneous multi casting or successive multi casting. Various methods suggested in JP-A 2005-104148 are usable in combination with the casting of the invention, the methods including construction of the casting die, decompression chamber, support and other mechanical elements, multi casting, stripping, stretching, conditioning for drying in respective steps, polymer film handling, winding after eliminating a curl for flatness, solvent collection, and polymer film collection. Those can be used in the present invention.

A. Support of Metal for Solution Casting

Suggested in JP A 2000-84960, U.S. Pat. No. 2,336,310, U.S. Pat. No. 2,367,503, U.S. Pat. No. 2,492,078, U.S. Pat. No. 2,492,977, U.S. Pat. No. 2,492,978, U.S. Pat. No. 2,607,704, U.S. Pat. No. 2,739,069, U.S. Pat. No. 2,739,070, GB A 640731 (corresponding to U.S. Pat. No. 2,492,977), GB A 735892, JP B 45-4554, JP B 49-5614, JP A 60-176834, JP A 60-203430, and JP A 62-115035.

B. Multi Casting

Suggested in JP B 62-43846; JP A 61-158414, JP A 1-122419, JP B 60-27562, JP A 61-94724, JP A 61-947245, JP A 61-104813, JP A 61-158413, JP A 6-134933; JP A 56-162617; JP A 61-94724, JP A 61-94725, and JP A 11-198285.

C. Specific Methods of Casting of Cellulose Esters

Suggested in JP A 61-94724, JP A 61-148013, JP A 4-85011 (corresponding to U.S. Pat. No. 5,188,788), JP A 4-286611, JP A 5-185443, JP A 5-185445, JP A 6-278149, and JP A 8-207210.

D. Stretching

Suggested in JP A 62-115035, JP A 4-152125, JP A 4-284211, JP A 4-298310, and JP A 11-48271.

E. Specific Methods of Drying

Suggested in JP A 8-134336, JP A 8-259706, and JP A 8-325388.

F. Drying of Specific Controls of Heat

Suggested in JP A 04-001009 (corresponding to U.S. Pat. No. 5,152,947), JP A 62-046626, JP A 04-286611, and JP A 2000-002809.

G. Drying in preventing wrinkles Suggested in JP A 11-123732, JP A 11-138568, and JP A 2000-176950.

Curls, thickness and their measurement of the wound polymer film are suggested in known documents mentioned in JP-A 2005-104148. These can be used in the present invention.

No. 1. Curls and Thickness of the Polymer Film

Suggested in JP-A 2003-011143, JP-A 2002-214432, JP-A 2002-221620, JP-A 2003-055477, and JP-A 2003-014556.

No. 2. Thickness and its Measurement

Suggested in JP-A 2003-098345, JP-A 2000-009931, JP-A 2001-343528 (corresponding to U.S.P. 2002/192397), JP-A 2002-122735, and JP-A 2002-194107.

At least one of the two surfaces of the polymer film is preferably processed by surface processing, because suitability for adhesion to optics such as a panel shaped polarizer element can be higher. Examples of the surface processing include vacuum glow discharge processing, atmospheric pressure plasma discharge processing, ultraviolet radiation applying processing, corona discharge processing, flame processing, acid processing, alkali processing and the like.

At least one of the two surfaces of the polymer film can preferably be coated with a functional material, to form a functional film including the polymer film as base, and one or two functional layers overlaid on the base. Examples of functional layers include an antistatic layer, hard resin layer, anti reflection layer, attachment facilitating layer, anti-glare layer, optical compensation layer and the like. For example, forming of the anti reflection layer can result in obtaining anti reflection film of which high image quality is available by preventing reflection of outer light. Methods of adding the surface processed functional layers to the cellulose ester film, and their various conditions are according to techniques suggested in JP-A 2005-104148. Those can be used in the present invention.

I. Plasma Processing in General

Suggested in JP A 6-123062 (corresponding to EP A 592979), JP A 11-5857, and JP A 11-293011.

II. Specific Methods of Plasma Processing

Suggested in JP A 2003-161807, JP A 2003-166063 (corresponding to U.S. Pat. No. 6,849,306), JP A 2003-171770, JP A 2003-183836, JP A 2003-201568, and JP A 2003-201570.

III. Glow Discharge Processing

Suggested in U.S. Pat. No. 3,462,335, U.S. Pat. No. 3,761,299, U.S. Pat. No. 4,072,769, GB A 891469; JP A 59-056430, and JP B 60-16614 (corresponding to GB A 1579002).

IV. Ultraviolet Processing

Suggested in JP B 43-2603, JP B 43-2604, and JP B 45-3828 (corresponding to GB A 1149812).

V. Corona Discharge Processing

Suggested in JP B 39-12838, JP A 47-19824 (corresponding to U.S. Pat. No. 3,849,166), JP A 48-28067 (corresponding to U.S. Pat. No. 3755683), and JP A 52-42114 (corresponding to U.S. Pat. No. 4,135,932).

VI. Matte Agents for Undercoats

Suggested in U.S. Pat. No. 4,142,894, and U.S. Pat. No. 4,396,706.

VII. Lubricants

Suggested in JP B 53-292, U.S. Pat. No. 3,933,516, U.S. Pat. No. 4,275,146; JP B 58-33541, GB A 927446 (corresponding to U.S. Pat. No. 3,121,060); JP A 55-126238, JP A 58-90633; JP A 58-50534; and European Patent Application 90108115 (corresponding to U.S. Pat. No. 5,063,147).

VIII. Polyorganosiloxanes as Lubricants

Suggested in JP B 53-292, JP B 55-49294, and JP A 60-140341.

IX. Antistatic Agents of Ionic Macromolecular Types

Suggested in JP B 49-23827, JP B 49-23828, JP B 47-28937; JP B 55-734, JP A 50-54672, JP B 59-14735, JP B 57-18175, JP B 57-18176, JP B 57-56059; JP B 53-13223, JP B 57-15376, JP B 53-45231, JP B 55-145783, JP B 55-65950, JP B 55-67746, JP B 57-11342, JP B 57-19735, JP B 58-56858, JP A 61-27853, and JP B 62-9346.

X. Polymer Films Coatable with Hard Coat Layers

Suggested in JP A 6-123806, JP A 9-113728, and JP A 9-203810.

XI. Photo Polymerizable Compounds

Suggested in JP A 50-151996, JP A 50-158680; JP A 50-151997 (corresponding to U.S. Pat. No. 4,058,401), JP A 52-30899 (corresponding to U.S. Pat. No. 4,256,828), JP A 55-125105; JP A 56-8428 (corresponding to U.S. Pat. No. 4,299,938), JP A 56-55420 (corresponding to U.S. Pat. No. 4,374,066), JP A 56-149402 (corresponding to U.S. Pat. No. 4,339,567), JP A 57-192429 (corresponding to U.S. Pat. No. 4,387,216); JP B 49-17040; and U.S. Pat. No. 4,139,655.

XII. Coatings for Preventing Reflection

Suggested in JP A 7-126552, JP A 7-188582, JP A 8-48935, JP A 8-100136, JP A 9-220791, and JP A 9-272169.

Various examples of liquid crystal display panels are known and suggested in JP-A 2005-104148, including TN type, STN type, VA type, OCH type, reflection type and the like. Any of those can be used in the present invention.

No. 1. Cellulose Ester Protective Films for Polarizers

Suggested in JP A 10-095861, JP A 10-095862, and JP A 09-113727.

No. 2. Uses of Cellulose Ester Films as High Performance Optical Elements

Suggested in JP A 2000-284124, JP A 2000-284123, and JP A 11-254466.

No. 3. Production of Cellulose Ester Films as High Performance Optical Elements

Suggested in JP A 2000-131523, JP A 06-130226, JP A 06-235819, JP A 2000-212298 (corresponding to U.S. Pat. No. 6,731,357), and JP A 2000-204173.

No. 4. Optical Compensation Sheets

Suggested in JP A 3-9325 (corresponding to U.S. Pat. No. 5,132,147), JP A 6-148429, JP A 8-50206 (corresponding to U.S. Pat. No. 5,583,679), and JP A 9-26572 (corresponding to U.S. Pat. No. 5,855,971).

No. 5. TN Type of LCD Panels

Suggested in JP A 3-9325 (corresponding to U.S. Pat. No. 5,132,147), JP A 6-148429, JP A 8-50206 (corresponding to U.S. Pat. No. 5,583,679), and JP A 9-26572 (corresponding to U.S. Pat. No. 5,855,971).

No. 6. Reflection Type of LCD Panels

Suggested in JP A 10-123478, WO 9848320 (corresponding to U.S. Pat. No. 6,791,640), JP B 3022477 (corresponding to U.S. Pat. No. 6,433,845); and WO 00-65384 (corresponding to EP A 1182470).

No. 7. Discotic Compounds as Coating Cellulose Ester Films

Suggested in JP A 7-267902, JP A 7-281028 (corresponding to U.S. Pat. No. 5,518,783), and JP A 7-306317.

No. 8. Characteristics of Optical Compensation Sheets

Suggested in JP A 8-5837, JP A 7-191217, JP A 8-50206, and JP A 7-281028.

No. 9. Production of Optical Compensation Sheets

Suggested in JP A 9-73081, JP A 8-160431, and JP A 9-73016.

No. 10. Use of Cellulose Ester Films in LCD Panels

Suggested in JP A 8-95034, JP A 9-197397, and JP A 11-316378. No. 11. LCD elements of guest-host reflection types Suggested in JP A 6-222350, JP A 8-36174, JP A 10-268300, JP A 10-292175, JP A 10-293301, JP A 10-311976, JP A 10-319442, JP A 10-325953, JP A 10-333138, and JP A 11-38410.

No. 12. Coating Methods

Suggested in U.S. Pat. No. 2,681,294; U.S. Pat. No. 2,761,791, U.S. Pat. No. 2,941,898, U.S. Pat. No. 3,508,947, and U.S. Pat. No. 3,526,528.

No. 13. Constructions of Overlaying Coatings

Suggested in JP A 8-122504, JP A 8-110401, JP A 10-300902 (corresponding to U.S. Pat. No. 6,207,263), JP A 2000-111706; JP A 10-206603 (corresponding to U.S. Pat. No. 6,207,263), and JP A 2002-243906.

No. 14. High refractive index layer and middle refractive index layer Suggested in JP A 11-295503, JP A 11-153703 (corresponding to U.S. Pat. No. 6,210,858), JP A 2000-9908, JP A 2001-310432, JP A 2001-166104 (corresponding to U.S. Pat. No. 6,791,649), U.S. Pat. No. 6,210,858, JP A 2002-277609 (corresponding to U.S. Pat. No. 6,949,284), JP A 2000-47004, JP A 2001-315242, JP A 2001-31871, JP A 2001-296401, and JP A 2001-293818.

No. 15. Low Refractive Index Layer

Suggested in JP A 9-222503, JP A 11-38202, JP A 2001-40284, JP A 2000-284102, JP A 11-258403, JP A 58-142958, JP A 58-147483, JP A 58-147484, JP A 9-157582 (corresponding to U.S. Pat. No. 6,183,872), JP A 11-106704 (corresponding to U.S. Pat. No. 6,129,980), JP A 2000-117902, JP A 2001-48590 (corresponding to U.S. Pat. No. 6,511,721), and JP A 2002-53804 (corresponding to U.S. Pat. No. 6,558,804).

No. 16. Hard Coat Layer

Suggested in JP A 2002-144913, JP A 2000-9908, and WO 00/46617 (corresponding to U.S. Pat. No. 7,063,872).

No. 17. Front Scattering Layer

Suggested in JP A 11-38208, JP A 2000-199809 (corresponding to U.S. Pat. No. 6,348,960), and JP A 2002-107512.

No. 18. Antiglare Characteristic

Suggested in Japanese Patent Application 2000-271878 (corresponding to JP A 2002-082207); JP A 2001-281410, Japanese Patent Application 2000-95893 (corresponding to U.S. Pat. No. 6,778,240), JP A 2001-100004 (corresponding to U.S. Pat. No. 6,693,746), JP A 2001-281407; JP A 63-278839, JP A 11-183710, and JP A 2000-275401.

No. 19. Dichroic Compounds

Suggested in JP A 1-161202, JP A 1-172906, JP A 1-172907, JP A 1-183602, JP A 1-248105, JP A 1-265205, and JP A 7-261024 (corresponding to U.S. Pat. No. 5,706,131).

No. 20. Various Devices and Films for Optics

Suggested in JP A 5-19115, JP A 5-119216, JP A 5-162261, JP A 5-182518, JP A 5-196819, JP A 5-264811, JP A 5-281411, JP A 5-281417, JP A 5-281537, JP A 5-288921, JP A 5-288923, JP A 5-311119, JP A 5-339395, JP A 5-40204, JP A 5-45512, JP A 6-109922, JP A 6-123805, JP A 6-160626, JP A 6-214107, JP A 6-214108, JP A 6-214109, JP A 6-222209, JP A 6-222353, JP A 6-234175, JP A 6-235810, JP A 6-241397, JP A 6-258520, JP A 6-264030, JP A 6-305270, JP A 6-331826, JP A 6-347641, JP A 6-75110, JP A 6-75111, JP A 6-82779, JP A 6-93133, JP A 7-104126, JP A 7-134212, JP A 7-181322, JP A 7-188383, JP A 7-230086, JP A 7-290652, JP A 7-294903, JP A 7-294904, JP A 7-294905, JP A 7-325219, JP A 7-56014, JP A 7-56017, JP A 7-92321, JP A 8-122525, JP A 8-146220, JP A 8-171016, JP A 8-188661, JP A 8-21999, JP A 8-240712, JP A 8-25575, JP A 8-286179, JP A 8-292322, JP A 8-297211, JP A 8-304624, JP A 8-313881, JP A 8-43812, JP A 8-62419, JP A 8-62422, JP A 8-76112, JP A 8-94834, JP A 9-137143, JP A 9-197127, JP A 9-251110, JP A 9-258023, JP A 9-269413, JP A 9-269414, JP A 9-281483, JP A 9-288212, JP A 9-288213, JP A 9-292525, JP A 9-292526, JP A 9-294959, JP A 9-318817, JP A 9-80233, JP A 9-99515, JP A 10-10320, JP A 10-104428, JP A 10-111403, JP A 10-111507, JP A 10-123302, JP A 10-123322, JP A 10-123323, JP A 10-176118, JP A 10-186133, JP A 10-264322, JP A 10-268133, JP A 10-268134, JP A 10-319408, JP A 10-332933, JP A 10-39137, JP A 10-39140, JP A 10-68821, JP A 10-68824, JP A 10-90517, JP A 11-116903, JP A 11-181131, JP A 11-211901, JP A 11-211914, JP A 11-242119, JP A 11-246693, JP A 11-246694, JP A 11-256117, JP A 11-258425, JP A 11-263861, JP A 11-287902, JP A 11-295525, JP A 11-295527, JP A 11-302423, JP A 11-309830, JP A 11-323552, JP A 11-335641, JP A 11-344700, JP A 11-349947, JP A 11-95011, JP A11-95030, JP A 11-95208, JP A 2000-109780, JP A 2000-110070, JP A 2000-119657, JP A 2000-141556, JP A 2000-147208, JP A 2000-17099, JP A 2000-171603, JP A 2000-171618, JP A 2000-180615, JP A 2000-187102, JP A 2000-187106, JP A 2000-191819, JP A 2000-191821, JP A 2000-193804, JP A 2000-204189, JP A 2000-206306, JP A 2000-214323, JP A 2000-214329, JP A 2000-230159, JP A 2000-235107, JP A 2000-241626, JP A 2000-250038, JP A 2000-267095, JP A 2000-284122, JP A 2000-292780, JP A 2000-292781, JP A 2000-304927, JP A 2000-304928, JP A 2000-304929, JP A 2000-309195, JP A 2000-309196, JP A 2000-309198, JP A 2000-309642, JP A 2000-310704, JP A 2000-310708, JP A 2000-310709, JP A 2000-310710, JP A 2000-310711, JP A 2000-310712, JP A 2000-310713, JP A 2000-310714, JP A 2000-310715, JP A 2000-310716, JP A 2000-310717, JP A 2000-321560, JP A 2000-321567, JP A 2000-329936, JP A 2000-329941, JP A 2000-338309, JP A 2000-338329, JP A 2000-344905, JP A 2000-347016, JP A 2000-347017, JP A 2000-347026, JP A 2000-347027, JP A 2000-347029, JP A 2000-347030, JP A 2000-347031, JP A 2000-347032, JP A 2000-347033, JP A 2000-347034, JP A 2000-347035, JP A 2000-347037, JP A 2000-347038, JP A 2000-86989, and JP A 2000-98392; and

JP A 2001-4819, JP A 2001-4829, JP A 2001-4830, JP A 2001-4831, JP A 2001-4832, JP A 2001-4834, JP A 2001-4835, JP A 2001-4836, JP A 2001-4838, JP A 2001-4839, JP A 2001-100012, JP A 2001-108805, JP A 2001-108806, JP A 2001-133627, JP A 2001-133628, JP A 2001-142062, JP A 2001-142072, JP A 2001-174630, JP A 2001-174634, JP A 2001-174637, JP A 2001-179902, JP A 2001-183526, JP A 2001-183653, JP A 2001-188103, JP A 2001-188124, JP A 2001-188125, JP A 2001-188225, JP A 2001-188231, JP A 2001-194505, JP A 2001-228311, JP A 2001-228333, JP A 2001-242461, JP A 2001-242546, JP A 2001-247834, JP A 2001-26061, JP A 2001-264517, JP A 2001-272535, JP A 2001-278924, JP A 2001-2797, JP A 2001-287308, JP A 2001-305345, JP A 2001-311823, JP A 2001-311827, JP A 2001-350005, JP A 2001-356207, JP A 2001-356213, JP A 2001-42122, JP A 2001-42323, JP A 2001-42325, JP A 2001-51118, JP A 2001-51119, JP A 2001-51120, JP A 2001-51273, JP A 2001-51274, JP A 2001-55573, JP A 2001-66431, JP A 2001-66597, JP A 2001-74920, JP A 2001-81469, JP A 2001-83329, JP A 2001-83515, JP A 2001-91719, JP A 2002-162628, JP A 2002-169024 (corresponding to U.S. Pat. No. 6,606,136), JP A 2002-189421, JP A 2002-201367 (corresponding to U.S. Pat. No. 6,093,133), JP A 2002-20410 (corresponding to U.S. Pat. No. 6,974,608), JP A 2002-258046, JP A 2002-275391, JP A 2002-294174, JP A 2002-311214 (corresponding to U.S. Pat. No. 6,841,237), JP A 2002-311246 (corresponding to U.S. Pat. No. 6,965,473), JP A 2002-328233, JP A 2002-338703, JP A 2002-363266 (corresponding to U.S. Pat. No. 6,894,141), JP A 2002-365164, JP A 2002-370303, JP A 2002-40209 (corresponding to U.S. Pat. No. 6,649,271), JP A 2002-48917 (corresponding to U.S. Pat. No. 6,628,369), JP A 2002-6109 (corresponding to U.S. Pat. No. 6,505,942), JP A 2002-71950, JR A 2002-82222, JP A 2002-90528, JP A 2003-105540 (corresponding to U.S. Pat. No. 6,689,479), JP A 2003-114331, JP A 2003-131036 (corresponding to U.S.P. 2003/031848), JP A 2003-139952, JP A 2003-153353, JP A 2003-172819, JP A 2003-35819, JP A 2003-43252 (corresponding to U.S. Pat. No. 6,552,145), JP A 2003-50318 (corresponding to U.S. Pat. No. 7,136,225), and JP A 2003-96066 (corresponding to U.S. Pat. No. 7,087,273).

Raw materials for producing the dope in the dope producing apparatus 20 are hereinafter described.

For a raw material of the dope, cellulose ester can be preferably used for obtaining high transparency. Examples of cellulose esters are cellulose triacetate, cellulose acetate propionate, cellulose acetate butylate and other cellulose esters of lower fatty acid. In particular, cellulose acetate is preferable. Specifically, cellulose triacetate (TAC) is desirable. Note that the dope in the present embodiment contains cellulose triacetate (TAC) as polymer. Preferably, 90 wt. % or more of the entirety of TAC should be particles of 0.1-4 mm.

Preferable examples of cellulose acylates satisfy all of the conditions I-III as follows for the purpose of high transparency:

2.5≦A÷B≦3.0  I

0≦A≦3.0  II

0≦B≦2.9  III

where A and B represent a degree of substitution of an acyl group formed by substituting hydroxy groups in cellulose. A represents a degree of substitution of an acetyl group formed by substituting hydroxy groups in cellulose. B represents a total degree of substitution of acyl groups having 3-22 carbon atoms.

The cellulose is constructed by glucose units making a beta-1, 4 bond, and each glucose unit has a liberated hydroxy group at 2, 3 and 6-positions. Cellulose acylate is a polymer in which part or whole of the hydroxy groups are esterified so that the hydrogen is substituted by acyl groups having two or more carbon atoms. The degree of substitution for the acyl groups in cellulose acylate is a degree of esterification at 2, 3 or 6-position in cellulose. Accordingly, when 100% of the hydroxy group at the same position is substituted, the degree of substitution at this position is 1.

The total degree of substitution DS2+DS3+DS6 for the acyl groups at 2, 3 or 6-positions is in the range of 2.00-3.00, preferably 2.22-2.90, and in particular preferably 2.40-2.88. The sign DS2 is a degree of substitution for the acyl groups at 2-position in hydroxy groups in the glucose unit. The signs DS3 and DS6 are degrees of substitution for the acyl groups at respectively 3 and 6-positions in hydroxy groups in the glucose unit. Further, a ratio DS6/(DS2+DS3+DS6) is preferably 0.28 or more, and particularly 0.30 or more, and especially in the range of 0.31-0.34.

An acyl group of only one example may be contained in the cellulose acylate of the invention. However, cellulose acylate may contain acyl groups of two or more examples. If two or more acyl groups are contained, one of the plural acyl groups should be preferably an acetyl group. Let DSA be a total degree of substitution for the acetyl groups. Let DSB be a total degree of substitution for other acyl groups at 2, 3 and 6-positions than the acetyl groups. The value DSA+DSB is preferably in the range of 2.22-2.90, and particularly in the range of 2.40-2.88.

Further, the DSB is preferably at least 0.30, and especially at least 0.70. Furthermore, the percentage of a substituent at 6-position in the DSB is preferably at least 20%, preferably at least 25%, especially at least 30% and most especially at least 33%. Further, the value DSA+DSB at 6-position is at least 0.75, preferably at least 0.80, and especially at least 0.85. Cellulose acylate satisfying the above conditions can be used to prepare a solution or dope having a preferable solubility. Especially, chlorine-free type organic solvent can be preferably used to prepare adequate dope. Also, the dope can be prepared to have a low viscosity, high solubility, and the suitability for filtration becomes higher.

Cellulose to produce cellulose acylates can be obtained any one of linter cotton and pulp cotton, but preferably can be obtained from linter cotton.

Examples of acyl groups in cellulose acylates having two or more carbon atoms can be aliphatic groups, aryl groups, and the like. For example, cellulose acylates may be alkyl carbonyl esters, alkenyl carbonyl esters, aromatic carbonyl esters, aromatic alkyl carbonyl esters, and the like of cellulose, and can further contain a substitution group. Preferable examples of groups include: propionyl, butanoyl, pentanoyl, hexanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, hexadecanoyl, octadecanoyl, iso-butanoyl, tert-butanoyl, cyclohexane carbonyl, oleoyl, benzoyl, naphthyl carbonyl, and cinnamoyl. Among those, particularly preferable groups are propionyl, butanoyl, dodecanoyl, octadecanoyl, tert-butanoyl, oleoyl, benzoyl, naphthyl carbonyl, and cinnamoyl. Further, specifically preferable groups are propionyl and butanoyl.

Details of cellulose acylates are according to various relevant techniques suggested in JP-A 2005-104148. Those examples and their various features can be used in the present invention.

I. Specific Examples of Cellulose Acylates

Suggested in JP A 57-182737 (corresponding to U.S. Pat. No. 4,499,043), JP A 10-45803 (corresponding to U.S. Pat. No. 5,856,468), JP A 11-269304 (corresponding to U.S. Pat. No. 6,139,785), JP A 8-231761, JP A 10-60170, JP A 9-40792, JP A 11-5851, JP A 9-90101, JP A 4-277530, JP A 11-292989, JP A 2000-131524, and JP A 2000-137115.

II. Specific Examples of Solvents for Esters and Their Dissolution

Suggested in JP A 10-324774, JP A 8-152514, JP A 10-330538, JP A 9-95538 (corresponding to U.S. Pat. No. 5,663,310), JP A 9-95557 (corresponding to U.S. Pat. No. 5,705,632), JP A 10-235664 (corresponding to U.S. Pat. No. 6,036,913), JP A 2000-63534, JP A 11-21379, JP A 10-182853, JP A 10-278056, JP A 10-279702, JP A 10-323853 (corresponding to U.S. Pat. No. 6,036,913), JP A 10-237186, JP A 11-60807, JP A 11-152342, JP A 11-292988, JP A 11-60752, JP A 2000-95876, and JP A 2000-95877.

Solvent as raw material of dope is preferably an organic compound in which polymer is soluble. The term of dope in the invention is used as mixture obtained by dissolution or dispersion of polymer in a solvent. It is possible to use a solvent with low solubility for polymer. Examples of solvents for preparing the dope include:

aromatic hydrocarbons, such as benzene and toluene;

halogenated hydrocarbons, such as dichloromethane, chloroform and chlorobenzene;

alcohols, such as methanol, ethanol, n-propanol, n-butanol, and diethylene glycol;

ketones, such as acetone and methyl ethyl ketone;

esters, such as methyl acetate, ethyl acetate, and propyl acetate;

ethers, such as tetrahydrofuran and methyl cellosolve.

It is possible selectively to use two or more of those by mixture. In particular, dichloromethane can be used to obtain dope with high solubility. The solvent in the cast film can evaporate to form the polymer film.

Halogenated hydrocarbons containing 1-7 carbon atoms are preferably used, for example, dichloromethane. Specifically, it is preferable in a mixed solvent to mix one or more alcohols containing 1-5 carbon atoms with the dichloromethane, for the purpose of high solubility, easy separability from a support for casting, mechanical strength of film material, and various optical characteristics of cellulose triacetate (TAC). Such alcohols are contained in the mixed solvent preferably in a range of 2-25 wt. %, and desirably in a range of 5-20 wt. %. Preferable examples of alcohols are methanol, ethanol, n-propanol, isopropanol, n-butanol and the like. Among those, specifically preferable alcohols are methanol, ethanol, n-butanol, and mixture of two or more of them.

For the purpose of minimizing influence to environment, solvents not containing dichloromethane are effectively used in the publicly suggested manner. Examples of compounds useful to this end are ethers having 4-12 carbon atoms, ketones having 3-12 carbon atoms, esters having 3-12 carbon atoms, and alcohols having 1-12 carbon atoms. Ethers, ketones, esters and alcohols of the examples may have a cyclic structure. Compounds having two or more functional groups of —O—, —CO—, —COO— and —OH, namely groups of ethers, ketones, esters and alcohols, can be used as a solvent. Furthermore, a solvent for use may contain other functional groups, such as alcoholic hydroxy groups. If a compound for a solvent contains two or more functional groups, a number of carbon atoms of the compound should satisfy a condition of a compound which contains a selected one of the two or more functional groups.

Various additives may be mixed in the dope for purposes, such as plasticizers, ultraviolet (UV) absorbers, deterioration inhibitors, lubricants, stripping accelerators, and other additives. Preferable examples of plasticizers are triphenyl phosphate, biphenyl diphenyl phosphate, and other phosphate esters, and diethyl phthalate and other phthalate esters, and polyester polyurethane elastomer.

Fine particles can be preferably added to dope for the purpose of preventing adhesion between polymer films, and adjusting a refractive index. Examples of materials of the fine particles are silicon dioxide derivatives. Examples of silicon dioxide derivatives include silicon dioxide, silicone resin in a honeycomb structure of three dimensions, and the like. Preferably, the surface of the silicon dioxide derivative is an alkylated surface. Fine particles processed by alkylation or hydrophobic modification have high dispersibility in solvent. Dope can be prepared without agglomeration of fine particles, to produce polymer film reliably. The polymer film can have high transparency with a reduced amount of surface defects.

An example of fine particles with an alkylated surface is Aerosil R805 (trade name) manufactured by Nippon Aerosil Co., Ltd., as a derivative of silicon dioxide with an octyl group on the surface. The ratio of the content of the fine particles relative to the solid content of the dope is preferably 0.2% or less for the purpose of obtaining polymer film with high transparency and with effects of adding the fine particles. An average particle diameter of the fine particles, in view of allowing passage of light without blocking, is equal to or less than 1.0 micron, preferably 0.3-1.0 micron, and desirably 0.4-0.8 micron.

It is preferable to use the TAC to prepare dope for the purpose of obtaining highly transparent polymer film. According to the embodiment, the dope containing TAC at a density equal to or more than 5 wt. % and equal to or less than 40 wt. % is obtained. A density of the TAC in the dope is preferably equal to or more than 15 wt. % and equal to or less than 30 wt. %, and desirably equal to or more than 17 wt. % and equal to or less than 25 wt. %. A density of the additive, especially a plasticizer, in the dope is preferably equal to or more than 1 wt. % and equal to or less than 20 wt. % in 100 wt. % of the solid content in the dope.

Uses of various materials in relation to the polymer have been suggested in JP-A 2005-104148, including solvents, plasticizers, deterioration inhibitors, ultraviolet (UV) absorbers, lubricants, stripping accelerators, optical anisotropy control agents, retardation control agents, dyes, release agents, and other additives.

I. Plasticizers

Suggested in JP A 4-227941, JP A 5-194788, JP A 60-250053, JP A 6-16869, JP A 5-271471, JP A 7-286068, JP A 5-5047 (corresponding to U.S. Pat. No. 5,279,659), JP A 11-80381, JP A 7-20317, JP A 8-57879, JP A 10-152568, and JP A 10-120824.

II. Deterioration Inhibitors and UV Absorbers

Suggested in JP A 60-235852, JP A 3-199201, JP A 5-190707, JP A 5-194789, JP A 5-197073, JP A 5-271471, JP A 6-107854, JP A 6-118233, JP A 6-148430, JP A 7-11055, JP A 7-11056, JP A 8-29619, JP A 8-239509 (corresponding to U.S. Pat. No. 5,806,834), JP A 2000-204173, and JP A 2000-193821.

In the dope production from cellulose triacetate, various techniques suggested in JP-A 2005-104148 for dissolution of materials and additives, filtration, elimination of bubbles, mixing of additives can be used.

No. 1. Dissolution Related to Casting

Suggested in JP A 9-95544 (corresponding to U.S. Pat. No. 5,663,310), JP A 10-45950, JP A 10-95854 (corresponding to U.S. Pat. No. 5,783,121), and JP A 2000-53784.

No. 2. Specific Preparing Methods of Solutions

Suggested in JP A 11-310640 (corresponding to U.S. Pat. No. 6,211,358), JP A 11-323017, JP A 11-302388, and JP A 2000-273184.

No. 3. Condensation of Solutions

Suggested in JP A 4-259511; U.S. Pat. No. 2,541,012, U.S. Pat. No. 2,858,229, U.S. Pat. No. 4,414,341, and U.S. Pat. No. 4,504,355.

Example 1

In FIG. 1, the cellulose ester film 37 was produced by the solution casting system 10. At first, the dope producing apparatus 20 supplied the casting die 24 with dope of a suitable amount through the feed block 22. The die slot of the casting die 24 ejected the dope on to the casting support drum 23 rotating continuously. A flow rate of the dope was so conditioned as to form the cellulose ester film 37 being 80 microns thick after drying. The die slot of the casting die 24 was 1.8 meters wide. The temperature of the dope being cast was conditioned at 36 deg. C. The inner temperature of the feed block 22 was conditioned at 36 deg. C. Also, the rear side of the bead was decompressed by conditioning the pressure of the decompressor 32 at 600 Pa.

The casting support drum 23 was a drum of stainless steel, and controllable by a driving device for rotational speed. Heat exchange medium or coolant was supplied by a heat exchange medium circulator (not shown) to the casting support drum 23, which was conditioned at the surface temperature of −10 deg. C. The casting chamber 11 was conditioned by the temperature adjuster 30 with the inner temperature of 35 deg. C.

The cast film 25 was cooled and gelled to have a self-supporting property. Then the stripping roller 26 stripped the cast film 25 to deliver the self-supporting cast film 25 a. The self-supporting cast film 25 a is moved to the transition region 12 where the fan or blower 36 blew evaporative gas at 40 deg. C. to the self-supporting cast film 25 a transported by the transport rollers 35, to dry the same.

The tenter pins 43 in FIG. 2 were pierced into the web edge portions 45 of the self-supporting cast film 25 a in the pin tentering machine 13, to transport the self-supporting cast film 25 a in the direction X. During the transport, the shifting mechanism 44 operated to stretch the self-supporting cast film 25 a in the direction X. The gas flow device 48 in FIGS. 2 and 3 was installed under the path for the self-supporting cast film 25 a. The aperture of the exhaust conduits 53 a was quadrilateral.

In FIG. 1, the self-supporting cast film 25 a exiting from the pin tentering machine 13 was sent to the clip tentering machine 14. Evaporative gas was blown to the self-supporting cast film 25 a while the web edge portions 45 of the self-supporting cast film 25 a were clamped and transported with stretch. The self-supporting cast film 25 a was dried to obtain the cellulose ester film 37. The web edge portions 45 of the self-supporting cast film 25 a or the cellulose ester film 37 were slitted by the web edge slitters 15 a and 15 b. A cutter blower (not shown) moved the web edge portions 45 by blowing into the film crusher 65, which ground the web edge portions 45 into chips or particles with an average area of 80 sq. mm.

Between the web edge slitter 15 b and the dryer 16, there was a pre-drying chamber (not shown), which heated the cellulose ester film 37 with evaporative gas of 100 deg. C. before drying in the dryer 16. The cellulose ester film 37 was transported through the dryer 16 by the rollers 67, and dried by the dryer 16. A temperature adjuster (not shown) conditioned the inner temperature of the dryer 16 to keep the surface temperature of the cellulose ester film 37 at 140 deg. C. Time of drying the cellulose ester film 37 with the dryer 16 was 10 minutes. The surface temperature of the cellulose ester film 37 was measured by a thermometer (not shown) disposed close to the surface of the cellulose ester film 37 and directly higher than the path of the cellulose ester film 37. The solvent gas created from the transition region 12, the pin tentering machine 13, the clip tentering machine 14 and the dryer 16 was collectively removed by adsorption and desorption of the adsorption solvent recovery device 69. An agent for adsorption was activated carbon. Desorption after the absorption was made by use of dry nitrogen. Then the collected solvent was dehydrated until the water content of water in the collected solvent became equal to or less than 0.3 wt. %.

The cellulose ester film 37 being dried was transported into a fluidity adjusting chamber (not shown) which was between the dryer 16 and the cooler 17. Air was supplied in the fluidity adjusting chamber with temperature of 50 deg. C. and a condensation point of 20 deg. C. Then air for fluidity adjustment was supplied directly to the cellulose ester film 37 with temperature of 90 deg. C. and humidity of 70% RH, to remove curls from the cellulose ester film 37. Then the cellulose ester film 37 was transported into the cooler 17, and was gradually cooled to a level equal to or lower than 30 deg. C.

Then the cellulose ester film 37 was transported into the winder 18. A pressure applied by the press roller 71 to the cellulose ester film 37 on the winding roller 70 was determined 50 N per meter. The winding roller 70 having a diameter of 169 mm wound the cellulose ester film 37. Tension was sequentially controlled, and set at 300 N per meter at the initial step of the winding, and set at 200 N per meter at the end of the winding. Thus, a roll of the cellulose ester film 37 was obtained.

The cellulose ester film 37 obtained finally was 80 microns thick. In the entirety of the solution casting process, an average drying rate of the self-supporting cast film 25 a or the cellulose ester film 37 was 20 wt. % per minute.

The following is components for preparing the polymer solution or dope.

Cellulose triacetate 100 parts by weight Dichloromethane 320 parts by weight Methanol 83 parts by weight 1-butanol 3 parts by weight Plasticizer A 7.6 parts by weight Plasticizer B 3.8 parts by weight UV absorber a 0.7 part by weight UV absorber b 0.3 part by weight Mixture of citrate esters 0.006 part by weight Fine particles 0.05 part by weight

In the list, the cellulose triacetate was powder particles having the following specifics—substitution degree: 2.84, viscosity average degree of polymerization (DP): 306, water content: 0.2 wt. %, viscosity of 6 wt. % dichloromethane solution: 315 mPa·s, average particle diameter of powder particles: 1.5 mm, standard deviation of the particle diameter of powder particles: 0.5 mm. The plasticizer A was triphenylphosphate. The plasticizer B was diphenylphosphate. The UV absorber a was 2(2′-hydroxy-3′,5′-di-tert-butylphenyl)benzotriazol. The UV absorber b was 2(2′-hydroxy-3′,5′-di-tert-amylphenyl) 5-chlorobenzotriazol. The citrate ester compound was mixture of citrate esters (mixture of citric acid, citrate monoethyl ester, citrate diethyl ester, and citrate triethyl ester). The fine particles were particles of silicon dioxide with a particle diameter of 15 nm, and Mohs hardness number of approx. 7. In the preparation of the dope, 4.0 wt. % of retardation control agent N-N-di-m-toluoyl-N-P-methoxy phenyl-1,3,5-triazine-2,4,6-triamine was added at the amount relative to the total weight of the polymer film.

Example 2

Example 1 was repeated with a difference in the gas flow in the pin tentering machine 13. In FIGS. 4 and 5, the gas flow device 75 was disposed under a path for the self-supporting cast film 25 a. The gaseous medium 77 was blown to the self-supporting cast film 25 a from the nozzles 82 a of the static pressure adjusting recess 82 and the nozzles 80 a of portions other than the static pressure adjusting recess 82.

Example 3

Example 1 was repeated with a difference in the gas flow in the pin tentering machine 13. In FIGS. 6 and 7, the gas flow device 90 was disposed under a path for the self-supporting cast film 25 a. The flow rate control unit 92 a in the first gas source 92 controlled so as to set a flow rate of the gaseous medium 96 smaller than that of the gaseous medium 100.

Example 4

Example 1 was repeated with a difference in the gas flow in the pin tentering machine 13. In FIGS. 8 and 9, the gas flow device 110 was disposed under a path for the self-supporting cast film 25 a. The shifting mechanism 118 kept the movable plate portions 116 shifted in the direction Z to lower the static pressure at the web middle portion.

In any of Examples 1-4, the static pressure distribution of the atmosphere under the self-supporting cast film 25 a was regulated in a range from −200% to +200% of the weight per area of the self-supporting cast film 25 a. The static pressure distribution was regularized, so that the web middle portion of the self-supporting cast film 25 a of in the pin tentering machine 13 was reliably prevented from protruding convexly upwards in the transport. The polymer film as a product was obtained with stably high quality.

Although the present invention has been fully described by way of the preferred embodiments thereof with reference to the accompanying drawings, various changes and modifications will be apparent to those having skill in this field. Therefore, unless otherwise these changes and modifications depart from the scope of the present invention, they should be construed as included therein. 

1. A web transport apparatus comprising: a transport mechanism for transporting web by retaining web edge portions of said web; a gas flow device for blowing gaseous medium to said web being transported, to float said web; and a static pressure adjuster for lowering static pressure of said gaseous medium to a web middle portion of said web with respect to a web width direction thereof, to regularize distribution of said static pressure in said web width direction.
 2. A web transport apparatus as defined in claim 1, wherein said gas flow device includes: a duct for introducing said gaseous medium; and a nozzle plate, positioned at a front end of said duct, having a nozzle, for blowing said gaseous medium through said nozzle.
 3. A web transport apparatus as defined in claim 2, wherein said static pressure adjuster limits said distribution of said static pressure to a value equal to or more than −200% and equal to or less than +200% per unit area of said web.
 4. A web transport apparatus as defined in claim 3, wherein said gaseous medium is evaporative gas, and said transport mechanism is constituted by a tentering mechanism.
 5. A web transport apparatus as defined in claim 3, wherein said static pressure adjuster controls a flow rate of said gaseous medium in said gas flow device with respect to said web width direction.
 6. A web transport apparatus as defined in claim 3, wherein said nozzle is constituted by plural nozzles; said static pressure adjuster includes an exhaust device, disposed to face said web middle portion between said plural nozzles, for exhausting said gaseous medium.
 7. A web transport apparatus as defined in claim 6, wherein said exhaust device is so constructed that a flow rate of exhausting said gaseous medium is variable.
 5. A web transport apparatus as defined in claim 6, wherein said plural nozzles include: a first nozzle group of nozzles opposed to said web edge portions; and a second nozzle group of nozzles, opposed to said web middle portion, and offset from said exhaust device.
 9. A web transport apparatus as defined in claim 3, wherein said static pressure adjuster includes a recess, formed in said nozzle plate, and opposed to said web middle portion.
 10. A web transport apparatus as defined in claim 3, wherein said nozzle is constituted by plural nozzles including: a first nozzle group of nozzles opposed to said web edge portions; a second nozzle group of nozzles, opposed to said web middle portion, for operating at a smaller flow rate of said gaseous medium than a flow rate of said gaseous medium of said first nozzle group, to constitute said static pressure adjuster.
 11. A web transport apparatus as defined in claim 10, wherein said duct includes: a first duct section for introducing said gaseous medium to said first nozzle group; a second duct section for introducing said gaseous medium to said second nozzle group; said static pressure adjuster controls said duct by setting said flow rate smaller for said second duct section than for said first duct section.
 12. A web transport apparatus as defined in claim 10, wherein a total aperture area of said second nozzle group is smaller than a total aperture area of said first nozzle group.
 13. A web transport apparatus as defined in claim 10, wherein a number of said nozzles in said second nozzle group is smaller than a number of said nozzles in said first nozzle group.
 14. A web transport apparatus as defined in claim 3, wherein said nozzle plate is constituted by plural nozzle plates, arranged in a transport direction of said web at a regular interval, disposed respectively to extend in said web width direction, for blowing said gaseous medium; said static pressure adjuster includes a movable plate portion disposed between said nozzle plates, a distance of said movable plate portion from said web being variable.
 15. A web transport apparatus as defined in claim 14, wherein said movable plate portion is set farther from said web than said nozzle plates.
 16. A web transport apparatus as defined in claim 14, further comprising an exhaust device, disposed through said movable plate portion, for exhausting said gaseous medium.
 17. A web transport apparatus as defined in claim 3, wherein said transport mechanism includes: first and second tenter pin groups, disposed to face respectively said web edge portions, respectively including plural tenter pins for piecing said web edge portions; a moving device for endlessly moving said first and second tenter pin groups along said web edge portions, to transport said web.
 18. A web transport apparatus as defined in claim 17, wherein said web is cast film, formed by casting cellulose ester solution containing cellulose ester and solvent, and having a self-supporting property.
 19. A web transport apparatus as defined in claim 18, wherein content of said solvent contained in said cast film is equal to or more than 130 wt. %.
 20. A solution casting process comprising steps of: casting cellulose ester solution on to an endlessly traveling support, to form cast film; stripping said cast film from said support; transporting said cast film by retaining web edge portions of said cast film; blowing gaseous medium to said cast film being transport for flotation; and lowering static pressure of said gaseous medium to a web middle portion of said cast film with respect to a web width direction thereof, to regularize distribution of said static pressure in said web width direction. 